The present invention relates to a kind of packaging bag and a manufacturing method thereof, and more specifically relates to an accordion-sides square-bottom bag and a manufacturing method thereof.
Square-bottom bags are widely used in various occasions for carrying objects or serving promotional purposes etc. An existing method of manufacturing an accordion-sides square bottom bag is to use a single piece of plane paper, make indentation lines on the paper, form a suitable outer contour by punching, fold the paper into a cylinder shape according to the indentation lines, glue the edges of paper to form a cylinder, make accordion folds on the cylinder, glue up the bottom part of the cylinder after folding the bottom edge of the cylinder by using glue or heat bonding method to form a square-bottom bag. Said manufacturing method is not effective. An alternative method is a continuous manufacturing method wherein rolled paper is used; edges of the rolled paper are sealed to form a cylinder and at the same time, accordion folds are made by using shaping die cutting molds; after that, cut the roll of paper into sections, fold the bottom part of each section, glue up each bottom part by glue or heat bonding to form a square-bottom bag for each section. Due to machining process of the entire roll of paper (e.g. by gravure) where edges of the paper are sealed along the entire roll of paper to form sections of cylinders and the accordion folds are continuously made, said method has a high efficiency. However, said method does not process indentation lines on the paper, therefore the bottom part of each section is not accurately formed, and the choices of materials for making the bag are limited. The two methods as described above generally produce a bag as shown in FIGS. 1-2. The formed bottom after folding process has a total of five layers, thereby thickening the bottom part; also, the layers are unevenly distributed, and the surface area for gluing or heat bonding is small, thereby leaving gaps in the middle and thus failing to achieve strong and reliable bonding; further when a plurality of such bags are stacked up, they take up a large amount of space.